#include<stdio.h>
void main()
{
	float mu=1;
	float sum=0;
	int d=1;

	while(1/mu > 0.0001)
	{
		sum = sum + d/mu;
		mu = mu + 2;
		d = -d;
	}
	printf("pai=%.4f\n",sum*4);
}
